Several applications are known to benefit from the measurement of a differential pressure. One example is a choke valve of a Christmas tree of a subsea wellhead assembly. The differential pressure across the valve can for example be monitored when closing the valve so as to obtain information about the functionality and the operability of the valve. Another application includes filter systems, in which the differential pressure across for example a filtration membrane can give an indication of the flow through the membrane and thus indicate clogging of the membrane.
Differential pressure (DP) sensors are known which measure the pressure difference between a first and a second input. As an example, in such differential pressure sensor, the pressure on each of the two inputs may be supplied to different sides of a membrane or diaphragm. If the pressure on both inputs is the same, then the diaphragm will essentially remain in an equilibrium position. Should the pressure on one input increase or decrease, the diaphragm will undergo a corresponding deformation or displacement which can be detected, for example by way of a strain sensor, capacitive detection, detection by piezo crystals or the like. The differential pressure sensor thus measures a differential pressure across the two inputs, irrespective of the absolute pressure at each input. Differential pressure sensors are generally suitable only for a limited range of differential pressures.
Furthermore, absolute pressure sensors are known which detect an absolute pressure value. Again, such absolute pressure sensor may be realized by a diaphragm and a strain sensor, with a vacuum, atmospheric pressure or any other desirable but fixed pressure prevailing at the other side of the diaphragm. Absolute pressure sensors can be capable of measuring pressures through a large pressure range. Yet such absolute pressure sensors suffer from drift, and are generally less accurate.
It is desirable to provide accurate pressure measurements over wide range of differential pressures. Furthermore, it is desirable to provide a pressure sensor with a long lifetime which is capable of giving accurate readings of differential pressure over the course of its life. It is also desirable to provide a compact pressure sensor that is suitable for subsea use.